A magnetic recording medium comprising a non-magnetic support having thereon a magnetic layer containing ferromagnetic particles composed of acicular crystals such as .gamma.-Fe.sub.2 O.sub.3, CrO.sub.2 and Co--Fe.sub.2 O.sub.3 dispersed in a binder has been widely used for magnetic recording and reproduction.
Recently, higher density recording has been strongly demanded for high volume recording and for minimizing the size of recording devices. In order to prepare a magnetic recording medium using conventional acicular magnetic particles which is suitable for higher density recording, it is necessary that the maximum dimension of the acicular magnetic particles be smaller than the recording wavelength or recording bit length. At present, acicular magnetic particles having a dimension of about 0.3 .mu.m have been realized and the shortest recording wavelength of about 1 .mu.m has been obtained.
In order to obtain a medium which can provide much higher density recording, it is necessary to further reduce the dimension of acicular magnetic particles. Such small acicular magnetic particles have a very thin thickness (100.ANG. or lower) and a very low particle volume (10.sup.17 cm.sup.3 or lower). Accordingly, problems that magnetic characteristics are decreased due to heat disturbance an effect on the surface (i.e., the effect in that the magnetic characteristics in surface portions of a magnetic medium are reduced because the spin of atoms which is present at the vicinity of the surface of the magnetic medium becomes unstable), and orientation cannot fully be conducted even if a magnetic layer is charged in the magnetic field.
To avoid the above defects, a magnetic recording medium using ferromagnetic particles of hexagonal system ferrite which is a tabular particle and has an axis of easy magnetization in a direction of perpendicular to the plate surface has recently been developed, as described in JP-A-58-6525 and JP-A-58-6526. The term "JP-A" as used herein means an unexamined published Japanese patent application. In accordance with the above medium, the average particle size of the ferromagnetic particles is 0.05 .mu.m or lower and higher density recording is possible.
Further, it is proposed that hexagonal system ferrite particles having a saturation magnetization of 30 emu/g or higher and a specific surface area of from 70 to 120 m.sup.2 /g be used to reduce noise and to increase S/N, as disclosed in JP-A-62-38531.
In a magnetic recording medium using hexagonal system ferrite magnetic particles, reproduction output and C/N can be improved by increasing a saturation magnetization, but, as ferromagnetic particles having a high specific surface area are used, dispersion is insufficient and it is difficult to simultaneously improve the running durability of a magnetic layer.